(a)[1]
Describe what is meant by the Doppler effect.
(b)[3]
A car moves at a steady speed along a straight road. Its horn emits a continuous sound with frequency of $400\,\text{Hz}$. A stationary observer by the roadside hears the horn at $360\,\text{Hz}$. The speed of sound is $340\,\text{m s}^{-1}$. Find the magnitude $v$, and the direction, of the car’s velocity relative to the observer.